The main theme of the series explores Sydney's obligation to conceal her true career from her friends and family, even as she assumes multiple aliases to carry out her missions. These themes are most prevalent in the first two seasons of the show. A major plotline of the series was the search for and recovery of artifacts created by Milo Rambaldi, a Renaissance-era character with similarities to both Leonardo da Vinci and Nostradamus. This plot and some technologies used in the series place Alias into the genre of science fiction.